As much as I hate to recommend it, Ficus repens (pumila) would be perfect for that spot. It's a very tough plant to control, but it will cover that wall in less than a year. Plant them every four feet in one-gallon cans.

What about vines? You don't say your location (city, zone) - that would be helpful to have. It would also be helpful to know which direction the wall faces and how much sun it receives. Lastly, some photos taken farther back to give us the overall perspective and one with something like a can of beans or soda would let us know the proportion of space with which you are working. It's hard to tell those things from photos. Without knowing that, I'm guessing that it is a very narrow space and you are looking for something that won't shed and make a mess in your pool. Some non-flowering vines would fit that description.

I don't think podocarpus would work well there, too narrow, but I'm interested to see what others say.

Carol in Jacksonville

Ah, Ricky, great minds think alike! We were posting simultaneously. :)

Thanks guys! I will post some more pictures when I get home this afternoon. Don't laugh at my greenish pool though. I'm in Orlando btw

There's also liriope &/or oyster plant.

Liriope

Oyster plant:

Ok sorry for the delay, there is about an 8" wide space at the narrowest part to plant stuff. Our pool pump went out last week so don't mind the greenish hue.

Carol, the holes are for a child fence that we have. But we don't have kids yet

What about pencil hollies?

Is there drainage under that small space? I hope so. What about Muhly Grass? It's simple to maintain as long as there is drainage and it gets pink seed heads in the fall, very pretty. Muhly Grass

I know that you want to "cover" the wall, but when I see your picture of the space I wonder why. The wall looks to be in good shape. I see plants at the top of the wall that might drape down a bit and shorter plants (such as those Carol suggested) in the narrow space. The plants would soften the hardscape and the wall would be a pleasing backdrop. Just my thought.

Planting trailing plants in the space above would be another way to cover that wall, albeit partially. Lantana & creeping juniper are 2 that come to mind. Lantanas will attract butterflies.

I agree i like the wall and something draping down would look fab. That purple or black potato vine maybe with oyster grass or purple queen growing below maybe? Or maybe mexican heather in the space below.

It's not that I really want to completely cover the wall, I just want to add some green to the concrete jungle that is my pool area. Thanks for the recommendations everyone! I'm researching all of them

Porterweed seems to grow well anywhere.

DunedinDan! Where have you been?! You gave me a little (1 foot?) loquat tree many years ago at a Tampa GW exchange. I kept it in a pot too long but alive, planted a couple of years ago, it's nose-high now. Hoping for bloom.